In the prior art, various devices have been proposed for the reduction of sound emitted by vacuum cleaner motors.
In Williams, U.S. Pat No. 4,015,683, there is disclosed a noise suppressor package to be attached to the air exhaust tubing of a vacuum cleaner, comprising an annular body which defines an axially extending bore to pass the exhaust. The body includes compressible foam segments which project radially inwardly at the bore to present a grooved inner surface, with the segments being axially elongated and circularly spaced. A tubular cover extends about the body and has a flexible neck at one end of the body. The neck is radially constricted about the exhaust tubing to retain the package to the tubing. The air exhaust passage runs directly through the noise suppressor package.
Oberdorfer, U.S. Pat. No. 4,665,581 pertains to a vacuum cleaner apparatus which has separate passages for the outgoing air from the blower and for cooling air for the blower motor, and has a number of turns in each of the passages. The turns develop increased air friction and back pressure. The passages have a plurality of variations in their cross-sectional area, and are provided with sound-absorbent linings which also create air friction and back pressure. The Oberdorfer apparatus appears to be of expensive construction and not disposable. The bending of high velocity air flow around a hard baffle-like surface creates noise and the hard surfaces are undesirable because they possess poor dampening characteristics with respect to low frequency sound.
A patent to Schulz, U.S. Pat. No. 4,475,264, discloses a dual inlet muffler assembly for a truck hot water vacuum extraction machine which has an elongated hollow plastic body which mounts a first exhaust pipe of L-shaped configuration passing completely through the body. Its inlet end is connected to the positive air pressure discharge of one vacuum pump connected to a closed dirty water vacuum dump tank for the hot water vacuum extraction machine. A second L-shaped exhaust pipe is reversely oriented within the hollow body and has a plugged end abutting the side of the first pipe near its inlet to the body. Both pipes are perforated within portions internal of the body and the hollow body is filled with glass wool to muffle the sound. The second pipe, at its inlet end, is connected to the positive pressure air discharging from a second vacuum pump also connected to the vacuum dump tank. The exhaust from the vacuum pumps is muffled with the air discharging through the perforations upstream of the plugged end of the second pipe passing through the glass wool, entering the perforations in the first pipe, and mixing commonly with the exhaust air flow carried by the first pipe. The disadvantages of Schultz include substantial back pressure, water build up in glass wool due to high humidity air flow, expensive construction, and the device is not of a low cost replaceable type.
The Brimberg U.S. Pat. No. 3,308,608 discloses providing an improved vacuum cleaner in which the housing is of light-weight construction so as to contribute to the portability thereof, and wherein the housing is said to have vibration-damping and soundproofing or sound absorbing characteristics in the form of a body of foamed, semi-rigid plastic, such as foamed polystyrene or polyurethane. The housing has compartments therein for accommodating the motor-fan unit and the dust collector or separator, with the outer surface of the foamed plastic body being covered by a layer of elastomeric material to resist damage to the foamed plastic body when the latter is subjected to impacts, as well as to avoid scratching or marring of furniture, walls or the like with which the housing is inadvertently contacted. The disadvantages of Brimberg are: not suitable for wet use--will retain moisture/water; flow baffles and restrictors will create back pressure; expensive construction; and not of a removable low cost disposable type.
Canaan et al., U.S. Pat. No. 3,882,961 pertains to an air-filtering, sound-attenuating muffler. The muffler includes an attenuator box and a multi-layer muffler filler. The layers of the muffler filler are reticulated polyurethane foam of varying pore densities. Air is directed through the muffler from the least dense to the most dense layer. The disadvantages of Canaan et al. include extensive back pressure problems--air flow forced through sound dampening media, the devise is not constructed for wet application, and is not of a replaceable los cost disposable type.
With the exception of Williams U.S. Pat. No. 4,015,683, the prior art units described in this application are of expensive permanent construction and all will develop, to various degrees, detrimental back pressure and thus affect the basic function and performance of any vacuum motor.